Co-channel interference (CCI) is constituted by one or more interfering signals within the frequency band of a desired signal in a communications system, and is a key factor that limits the capacity of cellular communications systems. The CCI can arise from communications in the same frequency channel in other cells of the system, or from other sources, so that its characteristics may be either similar to or different from those of the desired signal.
In International patent application No. PCT/CA96/00849 filed Dec. 18, 1996 in the name of Northern Telecom Limited (and in the corresponding U.S. patent application Ser. No. 08/730,828 filed Oct. 17, 1996 in the name of A. Abu-Dayya) entitled "Diversity Path Co-Channel Interference Reduction" there is described an arrangement in which diversity path signals, each comprising time division multiplexed (TDM) symbols in a time slot including known symbols, are combined with respective weights to reduce CCI. Such an arrangement is particularly applicable to TDMA (time division multiple access) cellular communications systems, in which the known symbols can for example comprise synchronization symbols. However, as AMPS systems are analog systems which do not use TDM and TDMA, and there are no known symbols such as synchronization symbols in time slots, such an arrangement can not be used for AMPS systems.
International patent application No. PCT/US93/00635, published as International Publication Number WO 93/19526 dated Sep. 30, 1993, entitled "Method And Apparatus For Estimating Signal Weighting Parameters In A Diversity Receiver" discloses a diversity combining receiver in which decoded data is re-encoded and the re-encoded data, and known data for example in a TDMA system, is used to determine new diversity weighting parameters, this process possibly being iterated.
It is also known from International patent application No. PCT/CA96/00672 in the name of W. Tong et al., published as International Publication Number WO 97/14227 dated Apr. 17, 1997, entitled "Co-Channel Interference Reduction", to reduce CCI in a cellular communications system using frequency modulation, such as AMPS, AMPS.sub.-- WD (Wide-band Data AMPS), and TDMA systems, by amplitude limiting complex signal samples of a received signal.
An object of this invention is to provide an improved method and apparatus for reducing CCI, applicable in an AMPS receiver.